Effect of divertor on tritium breeding in HELIAS

This study presents tritium breeding calculations for the five-period helical-axis advanced stellarator (HELIAS) using the Serpent2 code. To address the absence of a detailed divertor design, a simplified divertor model with a layered homogenized structure was integrated into the parametric geometry of the HELIAS. The impact of the divertor on the tritium breeding ratio (TBR) was assessed through a parametric study, varying divertor configurations, surface area, materials for both the divertor and breeding blanket, and the thickness of the breeding zone behind the divertor. Calculated TBR losses relative to full blanket coverage ranged from 4 % to 35 %, depending on the specified input parameters. The primary factors influencing TBR loss were the fraction of surface area occupied by the divertor and the volume of the breeding zone displaced by it. A linear relationship was observed between TBR loss and both the divertor area fraction and the reduction in breeding zone volume. Furthermore, water-cooled divertor configurations showed a more negative impact on TBR compared to helium-cooled, with effects comparable in significance to variations in area fraction. The difference in TBR loss between purely TBR-optimized divertor configuration and Wendelstein 7-X-like top-bottom configuration was less than 2 percentage points.